Winter 2001

TIMED heads for the atmospheric frontier

by David Hosansky

Scientists are looking forward to fresh data following the
launch of a new satellite expected to provide an unprecedented
view of the mysterious upper regions of Earth's atmosphere.
Launched on 7 December, TIMED (which stands for Thermosphere,
Ionosphere, Mesosphere, Energetics and Dynamics) is designed to
obtain a global picture of the atmosphere from roughly 60 to
180 kilometers (40110 miles) above Earth's surface.
Ground-based instruments can detect only a small portion of
this complex region, and sounding rockets provide just a brief
picture before falling back into the lower atmosphere.

"We're looking at weather at the edge of space," says Stanley
Solomon, a principal TIMED investigator at NCAR's High Altitude
Observatory. "This interface between what some people call the
atmosphere and some people call space is an extraordinarily
variable and dynamic region. I'm hoping to get a better
understanding of how the Sun controls it."

Solomon and other researchers hope to use data from the NASA
spacecraft to learn more about the temperature, wind, and
chemical composition of the upper atmosphere. That could
bolster communications networks, ensure that satellites stay on
course, and provide scientists with greater insight into human
influences on the atmosphere.

"There's never been a mission quite like this," says NCAR
director Tim Killeen. "We're going to be looking at a
fascinating part of the atmosphere, a real crossroads. TIMED
will for the first time really probe that region by exploring
the full range of atmospheric parametersdensity,
pressure, composition, vector winds, and other variables."
These data, he adds, "will then allow us to establish a pole-
to-pole climatology and really understand the region."

Killeen has been looking forward to the launch of TIMED since
he chaired a working group of scientists that began designing
the mission in the late 1980s. He is the principal investigator
for TIDI, the TIMED Doppler Interferometer, which will measure
globally the speed and direction of high-atmosphere winds.
Other NCAR scientists working on TIMED include Alan Burns,
Rolando Garcia, Maura Hagan, Roberta Johnson, Hanli Liu, Gang
Lu, Daniel Marsh, Arthur Richmond, Raymond Roble, Anne Smith,
and Qian Wu. According to Smith, one of the project's six
interdisciplinary investigators, "We will

use numerical models in conjunction with the TIMED observations
to investigate the physical mechanisms that affect energy and
composition [within the region]."

The space economy

The region under scrutiny by TIMED has important impacts on
orbiting vehicles and communications systems. When upper
atmospheric temperatures rise, the resulting expansion pushes
molecules to higher altitudes. This increased density exerts an
added drag on satellites and slows down their orbits. Changes
in the ionosphere can disrupt radio waves and affect the Global
Positioning System. In addition, bursts of solar radiation can
affect astronauts working on the space station.

"We have this large investment in a space-based economy," says
Solomon, "and we have to have a better understanding of issues
like the effects of atmospheric drag on orbits and the effects
of the ionosphere on communications." Knowledge of the upper
atmosphere lags behind that of the lower atmosphere by many
decades, he adds. Scientists lack the data to provide satellite
operators with even the crudest of forecasts about winds,
temperatures, and other conditions.

"Right now, it's like where we were 50 years ago when nobody
believed the weather forecasts," he explains. With TIMED,
Solomon believes that scientists will move to nowcasting the
upper atmospherethat is, reporting with some accuracy on
current conditions. In a few years, scientists may be able to
provide the equivalent of one-hour forecasts.

"We'll make some really fundamental advances in understanding
this region," he predicts. "Our goal is to take the next step
from basic research to being able to provide possible societal
benefits."

Just the facts

When: The TIMED satellite was launched on 7 December
2001 from Vandenberg Air Force Base, California. It will
collect data on its 388-mi (625-km) circular orbit around Earth
for two years. Another two years of data analysis will be
supported by TIMED's operations and data centers at Johns
Hopkins University.

How and who: Four instruments and associated teams, led
by the principal investigators below, will probe the mesophere
and lower thermosphere/ionosphere (MLTI).

GUVI: The Global Ultraviolet Imager is a spatial
scanning ultraviolet spectrograph designed to measure
composition and temperature profiles, as well as auroral energy
inputs (Andrew Christensen, The Aerospace Corporation)

SEE: The Solar Extreme Ultraviolet Experiment
consists of a spectrometer and a suite of photometers that will
measure solar soft X-ray, extreme-ultraviolet, and far-
ultraviolet radiation (Thomas Woods, University of Colorado)

TIDI: The TIMED Doppler Interferometer will
measure the wind and temperature profiles of the MLTI (Tim
Killeen, NCAR)

SABER: The Sounding of the Atmosphere using
Broadband Emission Radiometry mission will measure pressure,
temperature, key gases in the oxygen and hydrogen families,
infrared cooling, and effects of solar and chemical heating of
the MLTI (James Russell III, Hampton University)

Who else: More than 20 universities, laboratories, and
research firms. Collaborators include Johns Hopkins University;
the Universities of Alaska and Michigan; the University of
California, Berkeley; Utah State University; Rostock
University, Germany; and York University, Canada.